Diagnose the cause of the problem that led to the change of the DPF and make the repairs before fitting the new one, otherwise it will not work properly. Possible causes are: excess unburnt fuel and overheating in the DPF, misfiring, ignition system failure, towing, malfunctioning spark plugs or glow plug wire. Other causes may be oil or antifreeze entering the exhaust or sealing compounds that may have contaminated the DPF core, a pressure sensor fault or broken exhaust system hangers.